This issue came up in the comments to Ilya's post below, so I thought I'd point to a post of mine from a year ago on the subject. Short version: National Opinion Research Center surveys have for years gathered information on whether people believe that homosexual sexual relations are "always wrong" (the other possible answers to the question are that such relations are almost always wrong, only sometimes wrong, or not wrong at all). Here is the data from those surveys for 1973 and 2002, as reported by an American Enterprise Institute paper:

Age

1973

2002

Total

73

55

18-29

56

48

30-44

74

48

45-59

75

55

60 and over

89

68

This suggests that the group of people who were 18-29 in 1973 remained on average about as accepting of homosexual relations 29 years later, in 2002. The group who were 30 and above became slightly more accepting of homosexual relations, though only by a little. Neither the gay rights movement nor life experience seem to have made much of a difference to those age cohorts' attitudes. (Obviously they may have affected many individual members of each cohort, and could even have pushed tens of millions in one direction so long as they pushed a comparable number in the other; I'm speaking here of aggregate effects.)

Of course, it's possible that the attitudes about specific gay-rights questions (same-sex marriage, antidiscrimination laws, and the like) might be affected by age, even if attitudes about the morality of homosexuality are not. If you have similar age cohort studies that relate to those questions, I'd love to hear about them.

The Pew Research Center did an interesting poll on the subject recently, actually. The number of people who "strongly oppose" gay marriage has sharply declined in the last two years, from 42 percent in February of 2004 to 28 percent in March 2006. The greatest decline is among seniors, Republicans and moderate religious groups. Fully 58 percent of Americans age 65 and older strongly opposed gay marriage in 2004; only 33 percent are strongly opposed now. Seems to support the idea that old dogs can learn new tricks, if people make the case well enough.

Another picks this up:

The Pew study doesn't surprise me. It seems to me that people are more likely to have favorable viewpoints regarding issues associated homosexuality as we as a society talk about it more. Gay marriage or gay parents are no longer little discussed issues shoved in the very far back of the closet. The more those sorts of issues are discussed, the less bizare they sound. It's easy to whip people up into a fervor about something they haven't thought very much about and is never done. It's much harder to freak people out about something when they are informed (regardless of their conclusion) and when they see that other states and countries have done it and the world didn't come screetching to a halt.

To his credit, the first commentator provided a link to the study, and the study paints a rather different picture than the comment suggests. Strong opposition did fall from 42% to 28% between February 2004 and March 2006 -- but only after it had risen from 30% to 42% between July 2003 and February 2004. The change between July 2003 and March 2006 is thus a quite small and statistically insignificant -2%, not -14%. Similar results are present for the subgroups within the sample.